Method of stiffening unvulcanized rubber



Sept. 4, 1956 R. R. BARNHART ETAL y 2,761,857

METHOD oF STIFFENING uNvULcAmzED RUBBER Filed April 24, 1955 2Sheets-Sheet l .ATTORNEY Sept 4, 1955 R. R. BARNHART HAL 2,761,857

METHOD OF STIF'FENING UNVULCANIZED RUBBER Filed April 24, 195s 2sheets-sheet 2 IN V EN TORS ATTORNEY United States Patent O METHOD OFS'IIFFENING UNVULCANIZED RUBBER Robert R. Barnhart and Harry D. Glenn,Naugatuck, Conn., assignors to United States Rubber Company, New York,N. Y., a corporation of New Jersey Application April 24, 1953, serialNo. 350,842

3 Claims. (c1. 26o-83.3)

This invention relates to the stifening of u uvulcanized rubber andcompositions containing the same.

The art has been confronted with the problem of stiffening unvulcanizedrubber compositions in order to improve their manipulation in factoryoperations. Inmany operations it is desirable to impart stiffness to anuncured rubber stock by treatment with an extraneous material. Thechemicals, p,p-diaminodiphenylmethane and paminophenol, have been usedin the past for stiffening uncured rubber stocks but these chemicals areunsatisfactory in many cases because of their discoloring and stainingcharacteristics.

As used herein, the term stilfening includes both the imparting of anincreased viscosity to an uncured rubber formulation as well as thecounteracting of the softening of uncured rubber stocks which normallytakes place when such uncured stocks yare subjected to continued millingor mastication. In other words, our invention can be used to impartincreased viscosity to an existing rubber stock or to reduce the extentof softening of such a stock upon prolonged milling or mastication.Those skilled in the art will appreciate that stiffening chemicals 'areused in such a way that the over-all eect is that of rendering the stockmaterially stiler than it would be if it were prepared in the same waybut in the absence of the stifening chemical.

As is well-known in the art of rubber compounding, it is 1an easy matterto soften unvulcanized rubber stocks, this usually being effected bymerely milling the stocks to the desired lower viscosity. However, it isextremely difiicult to reverse the softening process and bring about anincrease in the stilness or viscosity of such stocks. In a given plantoperation, for various reasons such as excessive milling or thenecessity of re-using large volumes of scrap, the viscosity of a largemass of uncured rubber in process may become lowered too far forcommerci-al utilization. way of remedying it comprises blending thestock of excessively low viscosity with fresh stock of higher hardness;however, this is often out of the question in commercial operation dueto the excessive cost Ianti other factors. Therefore there has long beena need for a Ichemical which would markedly stiien uncured rubber stocksin a simple and economical manner by simple incorporation with suchstocks. To be commercially feasible, such la chemical must not have anyadverse effect upon the rubber or the nal vulcanizate and must be safeand easy to handle. It should also be effective when used in extremelysmall proportions so that the cost of using it will not be prohibitivelyhigh. It should also be free from discoloration yand should not stainlight colored material in contact with the `cured stock. Our inventionmeets 'all of these requirements and provides an extremely simple andsatisfactory solution of the problem.

The principal object of the present invention -is to provide ecientstilening agents for natural and synthetic rubbers including neoprene(polychloroprene) and synthetic rubbers containing at least by weight ofcorn- When such a situation arises, oneA vbined aliphatic conjugateddioletin, e. g., GR-S rand butadiene-acrylonitrile rubbery copolymers.The softening of these types of rubber on rubber mills and in internalmixers, e. g., of the type known as Banbury mixers, is necessary forproduction purposes; however, as is explained above, the uncured rubbermix as prepared often becomes of too low plasticity to be successfullyhandled in factory operations. The use of a stiifening agent isnecessary in such cases to overcome the undesirable low plasticity.

ln the accompanying drawings:

Fig. 1 is a graphical comparison of the eifect of varying amounts ofdihydrazine sulfate, dihydrazine oxalate, anhydrous hydrazine andphenylhydrazine upon the Mooney viscosity of natural rubber. The curvesfor hy- `tirazine itself and phenylhydrazine are given merely forcomparative purposes, since these chemicals are not embraced by ourinvention, hydrazine being unsatisfactory for many reasons andphenylhydrazine being a softener rather than a stiiener for rubber.

Fig. 2 shows graphically the effect of 0.1 part of dihydrazine oxalatein the milling of natural rubber. The curve is -a plot of the data inExample 1V below.

The present invention is based upon our discovery that dihydrazineoxalate and dihydrazine sulfate are very effective stitfening agents inunvulcanized rubber compositions. We have found that these salts ofhydrazine are particularly effective as 'stilfening agents when they areused in small concentrations. More specifically we have found that theyexert maximum stiffening action per unit of salt when they are used inconcentrations ranging om 0.01 to 0.1 part of actual hydrazine contentper parts of rubber. The marked effectiveness of such low concentrationsof dihydrazine oxalate and sulfate as stilfening agents, coupled withtheir good physical form and the relative ease and economy with whichthey can be manufactured, makes their use in rubber processingcommercially feasible.

Thus, dihydrazine oxalate and sulfate Iare valuable to rubbercompounders for preventing excessive softness and low viscosity inuncured rubber formulations in process, for example, in the case ofstocks embodying reworkable unvulcanized scrap rubber from the operationof cutting parts from calendered sheet. They are also useful forpreventing or reducing pressing and marking of stocks in process, forpreventing sagging or distortion of extruded uncured rubber goods, andfor improving the processing qualities of low grade crude rubbers bytoughening and hardening them in the uncured state. At the same timethey are completely free from the objectionable staining and discoloringtendencies of the previously used stilfen- -ing chemicals mentionedabove.

Dihydrazine oxalate is made by reacting two moles of hydrazine with onemole of oxalic acid. It is a white crystalline powder melting at 1Z0-130C., having a specie gravity of 1.66, having good storage stability, andexhibiting no physiological reactions upon the Workers making andhandling it. In addition, it dispersos readily in uncured rubber stocks.It contains about 41.5% of actual hydrazine.

Dihydrazine sulfate is made in a similar manner by reacting two moles ofhydrazine with one mole of sulfuric acid. It is a white crystallinematerial having good storage stability and exhibiting no physiologicalreactions upon workers making and handling it. It too disperses readilyin uncured rubber stocks. It contains about 39.5% of actual hydrazine.We prefer to market it in admixture with an inert carrier such as talcor clay. The use of such a carrier maintains for an indefinite periodthe free-owing characteristics of the material despite the normallydeliquescent nature of pure dihydrazine sulfate and is not objectionablebecause the amount thereof introduced into the rubber stock is so smallas to be negligible. Typically we market a mixture of about 26% ofdihydrazine sulfate and 74% of inert carrier.

The amount of dihydrazine oxalate or sulfate used is extremelyimportant. If an amount less than that corresponding to 0.01 part ofactual hydrazine per 100 parts of rubber is used, the stiiening actionproduced will not be sufficiently great to be of commercial value. Onthe other hand, as the amount is increased materially above thatcorresponding to 0.1 part of actual hydrazine per 100 parts of rubberthe stiffening action falls 0E rapidly so that amounts in excess ofthose corresponding to 0.1 part of hydrazineare not ordinarilycommercially feasible.

Generally speaking, within the above range the stift'ening action ot thedihydrazine oxalate or sulfate increases as the amount increases,reaching a peak in the neighborhood of, or at a value somewhat below 0.1part of actual hydrazine content per 100 parts of rubberl and thenfalling oi rather sharply although continuing to stffen to a markedextent at concentrations above 0.1 part of actual hydrazine. Thus vthecost for the chemical per unit of stitening action is lowest in therange of from 0.01 to 0.1 part of actual hydrazine content and usuallybecomes undesirably high as the 0.1 part figure is exceeded. For thisreason and because maximum stilening is generally attained at not overthe 0.1 part ligure, we

been broken down for 3 minutes in a 2B Banbury mixerat 116 R. P. M., andmixing therein was continued for 17 additional minutes. The stocktemperaturey approximated 240 F. At the end of the 17 minute mixingcycle the mix was discharged. The Mooney viscosity was measuredimmediately after mixing and afterl a standing period of 24 hours. InFig. 1 the viscosities afterl the 24 hour rest period are plottedagainst concentration of the chemical in terms of actual hydrazinecontent. The

data were as follows:

smoked sheet 100.0 100.0 100.0 100.0 mud? prefel: to Operate Wlthm therange glvfm abofe' Dihydrazine oxalate.-- 0. 072 0. 241 0.795 2. 4i

Dihydrazine oxalate and sulfate have a slight activating effect on therate of cure but this is beneiicial rather than harmful since excessmilling tends to slow curing rates in some rubbers. If desired, thisactivating or ac- N 0 P celerating effect can be otset by the use of alower a ti smoked sheet 100.0 100.0 100.0 100.0 concentration ofaccelerator or by the ddi on of an Phenylhydrazme a 101 0.338 L12 3.38acidic material.

MooNEY VISCOSITiEs-n HRS. AFTER MIXING Parts Pure Hydra- Dihydia-Dihydra- Pheny]- Hydrazlne Stock zine Stock zine Stock zine Stockhydrazine as 3s 4s 35.5 62 22 40.5 i4 39 MOONEY VISCOSITIEs-ai HRS.AFTER MIXING Parts Pure Hydra- Dhydra.- Dihydra- Phenyl- Hydrazine Stockzine Stock zine Stock zine Stock hydrazine Sulfate Oxalate In contrastto hydrazine itself, which is a corrosive liquid impractical for use inconventional rubber compounding, dihydrazine oxalate and sulfate aresupplied in the form of non-corrosive powdered solids which can beeasily shipped, handled, weighed out and incorporated Vou the rubbermill or in the Banbury mixer using conventional rubber compoundingprocedure. In addition,

-asis shown in Fig. 1 of the accompanying drawing and From the foregoingdata and from Fig. 1 of the drawings it will be seen that the stiienngaction of anhydrous 60 hydrazinereached a peak somewhere in the vicinityof 0.1 part. Above this level, the stiening action was less pronouncedand'at 1.0 part it exhibited virtually no stiteningaction. Dihydrazinesulfate and oxalate both stitened the stock throughout the range oftesting and amounts of the salts which furnished 1.0 part of actualhydrazine caused aconsiderably higher Mooney viscosity than the blank.Both dihydrazine lsulfate and oxalate imparted a considerablygreaterstitening action than equivalent amounts of hydrazine itself at all con.centrations except inthe case of the 0.1 part level immediately aftermixing;.even in this case, after standing 24 hours the Mooney viscosityof stock C made with hydrazine itself was substantially lower than thatof cor- Aresponding stocks Gand lK made with the hydrazine 75 salts. Itis particularly noteworthy that in all cases dihydrazine sulfate andoxalate were much more eiective Stieners than Ahydrazine at the lowconcentration of 0.03 part of actualhydrazine furnished, their stiteningaction being very pronounced atthis low level. This is important becauseit enables the rubber compounder to obtain a greater stiffening actionat lower expense. Phenylhydrazine, even in very low concentrations,plasticizes the stock and continues to do so as the concentration isincreased.

In practicing our invention the dihydrazine oxalate or sulfate isintimately incorporated with the uncured rubber in the presence orabsence of conventional compounding ingredients including fillers,vulcanizing agents, especially sulfur, accelerators of vulcanization,softeners, anti-oxidants, etc. The incorporation of the dihydrazineoxalate or sulfate with the rubber is most conveniently accomplished bysimply milling or masticating them together in the conventional mannerused in the rubber industry, for example, using an ordinary two-rollopen rubber mill or using an internal mixer, such as a Banbury mixer,for a suitable period of time, typically ranging -from 2 to 30 minutes,suilcient to give a uniform homogeneous mixture. The stiffening actionapparently is facilitated by at least some degree of heat which is mostconveniently applied during mastication or milling. r[he degree of heatgenerated when the stock is milled on the ordinary open rubber mill issuicient to expedite the desired stiiening action upon the rubber eventhough the rubber mill be cooled in the ordinary mannerv by circulatingcold Water through the rolls Whereby the temperature of the rolls doesnot exceed 100 F. The temperature to which the stock is heated willtypically range from about 100 F. upwardly to any desired temperature.The temperature to which the stock is heated must not be so high as toinjure the rubber. An upper of 350 F. is generally applicable. Althoughthe application of at least a moderate degree of heat expedites thestiffening action of the dihydrazine oxalate or sulfate, neverthelessexposure of the mixture to room temperature alonewill cause the salt toexert a substan- -tial stiening elect, especially when the mixture isa1- lowed to stand for several hours.

After the dihydrazine oxalate or sulfate has been thoroughly andintimately incorporated into the rubber, which operation is usuallycompleted within a 'few minutes, the time required for suchincorporation varying with the type and size of milling or masticatingequipment available, the size of the batch, and other factors, theresulting mixture can be further masticated or can be allowed to remainin the static condition; during such further mastication or during suchholding in static condition, the hydrazine salt generally brings about asubstantial additional stiffening action upon the rubber. 'Thisadditional stiffening action is particularly noticeable in the case ofmaintenance of the stock in static condition. Such additional stifleningupon such stationary holding of the stock is escially advantageousduring subsequent processing or handling ofthe stocks priortovulcanization because it is achieved at low cost and additionlallyserves to counteract or prevent sagging or other distortion of -thestocks during subsequent processing operations.

The further mastication or static maintenance of the stocks having thestilening agent intimately incorporated therein can be carried out attemperatures ranging from room temperature upwardly to the point ofthermal decomposition of the rubber and for any suitable Iduration oftime. It will be understood that the action of masticating itself causesa substantial softening of the rubber which may take place to such anextent as to result in an over-all softening of the stock during suchmastication, although such softening because of mastication is partiallycounteracted by the stiftening eiect of the dihydrazine oxalate orsulfate, so that at the end of mastication the stock is substantiallystiler than it would have been had the hydrazine salt not been present.It will be understood that the principal, if not the sole, purpose ofmastication of the stock after the sn'iiening agent has been intimatelyincorporated with the rubber Will be to effect the incorporation ofcompounding ingredients not previously incorporated. It will also beunderstood that mastication of the stock should be discontinued at apoint at which the stock has a viscosity or stiffness greater than itwould have had in the absence of the stiffening agent so that thebenefits of the stiiening action of the latter are obtained duringsubsequent processing operations. In other Words, We limit masticationafter incorporation of the dihydrazine oxalate or sulfate so as to avoidworking out completely the stiifening action thereof.

As has been indicated, the present invention is particularly applicableto natural rubber, neoprene (polychlorobutadiene) and synthetic rubbersWhichcontain at least 25% of combined aliphatic conjugated dioleiin, e.g., butadiene or isoprene. Examples of such synthetic rubber to whichthe invention is particularly applicable include butadiene-styrenerubbery copolymers, rubbery polybutadiene, rubbery polyisoprene andbutadieneacrylonitrile rubbery copolymers. Our experience has indicatedthat While dihydrazine oxalate and sulfate will stiften butyl rubber,which can be described generally as a low temperature copolymer ofisobutylene and `a small amount (usually from 0.5 to 5%) of butadiene orisoprene, it is not ordinarily commercially desirable to stiiien butylrubber stocks by means of our invention because the low permeability ofbutyl rubber to the gases liberated by decomposition of the hydrazinesalt during processing (including curing) causes `such gases to beretained in the final cured article resulting in undesired porosity.Consequently, the use of our stiffening agents iu butyl rubber stocks isnot recommended.

In practicing the invention, We typically masticate the mixture of thestiiening agent and the rubber, with or Without other compoundingingredients, on an open rubber mill or in an internal mixer, e. g., aBanbury mixer, incorporating sulfur and other compounding ingredients atany suitable point in the process, sheet out the resulting mixture,shape and vulcanize. The mixing iS often done at temperatures rangingfrom F. to 300 F. Those skilled in the art will appreciate thattheprocessing is so carried out that the stiiness of the unvuleanizedrubber after mastication and incorporation of compounding ingredients inpreparation for shaping and vulcanization is substantially greater thanit would be were the stiiening agent not employed. lt will also -beunderstood that processing and vulcanization ,are so conducted that thevulcanizate does not occlude any gases which may be liberated as aresult of the presence of the stiflening agent. Those skilled in the artwill recognize that any such gases can be easilyv caused to escape soY,that a non-cellular vulcanized article is obtained. Because vtheamount of the hydrazine salt used in practicing the invention isextremely small, and because ordinary incorporating and vulcanizingtechniques canreasily be so adjusted as to make provision for the escapeof any small amount of gases liberated by the hydrazine salt, nodiiiculties in this connection will ordinarily be encountered.

The present invention is particularly applicable -in the manufacture ofrubber lthread which is usually made from an almost pure gum stock, i.e., a stock free from l'illers in more than pigmenting amounts. Forexample, the use of 0.04% of dihydrazine oxalate or sulfate in themanufacture of cut rubber thread, gives an extremely advantageousstiften-ing effect before v'ulcanization. The invent-ion can also beadvantageously used inthe manufacture of ordinary rubber stockscontaining considerable proportions of reinforcing or non-reinforcingfillers, e. g., carbon black, clay, titanium dioxide, etc.

The present invention is useful in stitening stocks; which do notcontain substantial proportions of carbon black, i. e., the so-callednon-blac stocks. Our dispense.

-Pine tar =`Mercaptobenzotluazole VMooney Viscosity 7 covery of themarked ability of our hydrazine salts to stiifen rubber in thesubstantial absence of carbon black is'. highly advantageous sinceVthere are many stocks in which thepresence of substantial proportionsof carbon black is undesirable. Generally speaking, our hydrazine saltsshow a substantially greater st-iifening action in the case of carbonblack-containing natural rubber and GR-S stocks than with thecorresponding non-black stocks. In lthe case of butadiene-acrylonilrilerubbery copolymer stocks, however, the stiiening action of our hydrazinesalts is substantially greater in the case of the non-black stocks thanwith the black stocks.

The use of our hydrazine salts as stiftening agents for rubber inaccordance wit-h our invention is highly adl vantageous. They areeffective stitleners in a wide variety `of rubber stocks. They arerelatively non-pigmenting and non-discoloring and are non-staining tocloth and lacquers. They prevent sagging or distortion of the design ofextruded products. They prevent liner marking `or attening of embossedfinishes. Their use enables increased re-use of cutting scrap whichnormally becomes too soft after repeated reprocessing, thereby reducingex- Their use enables the use of the less expensive soft grades ofrubber due to the fact that our hydrazine salts exert a toughening andhardening action upon such types of rubber when in the uncured sta-te.They are ef fectivewit-h a very wide range of vulcanizing agents andaccelerators and in faetvin almost any uncured rubber stock. Numerousother advantages of our invention will be apparent to those skilled inthe art.

'Ihe following examples illustrate the invention more fully. All partsare by weight. All Mooney viscosities 4were measured at 212 F. with thewell-known Mooney plastometer in the standard manner.

Example I A rubber masterbatch was prepared in accordance with thefollowing recipe:

Par-ts Rubbersmoked sheets natural rubber 100.0 Carbon black 45.0 Zincoxide 5.0 3.5 3.5 3.0 1.0

To a portion of the above masterbatch which had been broken down for 17minutes there was added dihydrazine oxalate in .the proportion shownbelow to form Stock B. Stock A was the control. Both stocks werethoroughly mixed on a G-160 F. rubber mill and sheeted out. Sanples weredied out and the Mooney viscosity measure Zinc salts of cocoanut fattyacids Sulfur Masterbatch 161. 0 Dihydrazine Oumlnfp Example II 'Illefollowing example illustrates the ability of dihydrazine oxalate tostiifen smoked sheets (in the absence of a ller) when the stock issubjected to ten minutes mastication on a rubber mill at mill rolltemperatures of vless than 100 F. and at 300 F. The dihydrazine oxalatewas incorporated in the following manner; .the smoked sheets were firstbanded on the open rubber mill at the specified temperature; as soon asthe rubber had formed a band, the oxalate was added to the band andthoroughly incorporated. The temperature of the stock was probablyslightly above 100 F. in the rst series of runs because of the heatgenerated bythe mastication. Generally speaking, the time required tointimately incorporate vthe VF' '.G i I.'

smoked sheets 100.0 `Y100.0 `100.0 100.0 100.0 Dihydrazine Oxalate 0.10. 25 0. 5 l. 0

MOONEY VISCOSITIES After milling for ten minutes on a cold mill (at lessthan 100 F.) 28 37 y38.5 40.5 36.5 Aftermilling for ten minutes on 8 300F. mill 79 101 96 94 89. 5

Example'lll Two masterbatches were mixed in accordance with thefollowing recipes. GR-S was used as the polymer. The effect ofdihydrazine oxalate as a stiffening agent is illustrated in the presenceof black and non-black fillers:

'The masterbatches were eachdivided in equal portions and to one portionof each masterbatch was added the stilfening agent in the proportionshown below. All the portions were milled three minutes on a 15G-160" F.rubber mill. Mooney viscosities were then run on the milled stocks.

L M N O Non-black Masterbatch 244. 25 244. 25 Black Masterbatrh 166. 6166. 6 Dhydrazine @miam 0. 1 Y 0. 1

Compounded Mooney Viscoslties. 46. 5 55 34. 5 48 It isrevident that thedihydrazine oxalate exhibited a greater stiffening eect in the case ofthe carbon blackcontaining GR-S stock than in the case of the non-blackv GR-S stock.

Example IV Smoked sheets were masticated at 300 F. in a laboratory sizeBanbury mixer for 5, 10 and 15 minutes. In one case the smoked sheetsalone were masticated while in a comparative experiment the smokedsheets together with 0.1 part of dihydrazine oxalate per 100 parts ofrubber were employed. The Mooney viscosities were determined at the endof the 5, l0 and 15 minute periods.

The results were as follows:

9 The above data (which are plottedin Fig. 2 of the drawings) show theeffect of dihydrazine oxalate in preventing excessive softening ofuncured rubber during hot processing.

Exam le V 5 reinforced with a furnace type of carbon black (known as pHMF). The data were as follows:

TWO commerclal types of neoPrene .lamely Neopren? MOONEY vIsoosITY oNEANBURY MIXED BU'IADIENE RT and Neoprene W Wel-e admlxed Wlth 0.1 Of dl-ACRYLONITRILE POLYMER STOCKS liydrazine oxalate per 100 parts of rubberin the same way as in Example Il, on an open rubber mill, the tem- 10 -bk s B1 k st k perature of the mill rolls being 250 F. The following Nonlac tack l ac oc table shows the Mooney viscosity of control samples and17 of +0 17 of of the samples containing the dihydrazine oxalate afterBlank dihy'drzine Blank dihy'drzine different periods of milling at 250F. 0mm Oxalate o FT M LL 2' F. 15 MOONEY vis osITIEsA ER I ING A1 n076.5 124 87 106 Neoprene RT Neoprene W Example 1X M dP i 42 Esse olymer20 To separate portions of a natural rubber masterbatch +017 of +017 ofmade with smoked sheets according to the formulation B11-.nk dinyerzinemank dihy'tnnne given in Example l, varying amounts of dihydrazineOxalte malate oxalate were incorporated in the sarne manner as inExample I. The Mooney viscosities of samples vof the e 5' 20 F. Munn i418.5 41.5 52 i/5505 F. gg- 12 20. o 36 7 5 25 mixes were determined.Samples were cured 45 minutes 15'/250 F. Miuing 15.5 23.5 34 525 at 30lbs. steam pressure. The data on these experiments were as follows:

Example VI Y In the same way as 'in Example V the stiffeniug action 30 PQ R s -of dihydrazine oxalate was tested in both regular GR \r 1R bb M tb n and in so-caued cold GR-S X-478), the milling beniinie Onn 165 mi?13.1.22 1652 o ing done at 250 F. The following data were obtained.Mooney Viscosis of Uncured Massed Polymer a5 49 12.90l ,41570 '418004:59a

40 645 52a e30 v58o 0.1 f 0.1 f Blank dilgydzine Blank dydzineT50ofvn1canizates arssofz, 1.5 -28 5.6 -04 oxalate oxalate A l o Theeffect of increasing amounts of dihydrazine oxalatein foi/2g? nlgg'" n'ig g increasing the viscosity or reducing the plasticity of the 15'/250F. Mi11ing 32 45 46 50 45 stocks is readily apparent. It will also beseenl that the physical properties of the vulcanizates obtained from theExample VII stocks containing dihydrazine oxalate are not adverselyaffected b the dih drazine oxalate.

In the same way as 1n Examples V and VI, the stiffeny y ing action ofdihydrazine oxalate upon rubbery buta- Example X diene-acrylonitrilecopolymers was determined. I Two In the following hot air and hotairfammonia cured COmmOBlS/lused Butfdene'acrylmmle COPOiYmeS ldem'footwear stocks, the marked ability of dihydrazine oxalate ed 15 A and Bwere used- The fonowmg data were to rm the stocks (thereby reducingmarking and press- Obtalnedt ing) and to retard. `the `breakdown of thestocks (thereby MooNEY vIsoosITIEs AETEE MILLING AT 250 F. 55 allovw'ngthe use of reworkable scrap in repeated calenderings) is illustrated.Only a very small amount Butadiene- Butadiene- (0.1%) of dihydrazineoxalate is needed to accomplish Acrylomtrle., Acrylomtrll thisstiffening effect. There were rst prepared two Copolymer A Copolymer B emasterbatches having the following formulations: Massed Polymer 92 78 60Masterbatches Blank diioi? 9i Blank dilno'fiiziii y y 221118 Y BZ 6oxalate oxalate Egfnlilria Cured a ist a 5 lng--- Irv/250 F. Milling110.5 i2i 01 08 kfff: j logjg mgjg l47.0 47.0 5.0 5 0 Example VIIIMercaptobenzoth ol 1.25 Benzothiazyl'D'isulde" 0.40

Non-black and carbon black-containing butadiene- 'SIelrmethyltbv-iramMonosulde-- 0.125 0.02 acrylonitrile copolymer stocks, With and without0.1% u ur L65 165 of dihydrazine oxalate based on the copolymer, were161.025 16.0.07

mixed in the laboratory Banbury mixer. Copolymer A (as used in ExampleVII) was employed. The following Mooney viscosity data show a greaterstiening effect for dihydrazine oxalate in filler-containing stocks thanwhen used Vin the copolymer .only (as in Example The dihydrazineoxalate'was also .more Yeffective in the non-black stock than -it was inthe black'stock which was These masterbatches were mixed-Withdihydrazine oxalate in the proportions shown in the following table. The

:parts of rubber polymer.

method of incorporation was the same as in Example I. The Mooneyviscosities of the resulting mixtures were determined. Samples werecured by beingk raised to a temperature of 260 F. over-'30 minutesfollowed vby holding at that temperature for 40 minutes. The data on theuncured stocks and on the vulcanizates were as follows:

Hot Air Cured Masterbatch 161.025 161.025 161.025 Hot A1rAmmonta CuredMasterbatch 160.07 160.07 160.07 Dlhydrazine Oxalate 0.1 1.0 0 0.1 1.0

MOONEY VISCOSITIES Calendered Stock 48 63 68 51 62.5 62.5 ResheetedStock 45.5 58.5 62 48.5 57 60 MOONEY SCORCH AT 250 F.

3 Point Rise Above Minimum Y et 9 5% 38% 26 l0 23 Point Rise AboveMinimum feet 2 1% 8% 12% 2 UNAGED TENSILE PROPERTIES, P. S. I.

400 420 420 470 470 410 1,030 1,075 1,150 1,330 1,330 1,250 2, 740 2,9302,930 2, 690 2,720 2, 290 713 703 695 680 660 625 T-5o at 500% -12.o11.e 11.2 i -1.4 i -1.s l 1.6

It will be seen that in these stocks the stiilening eiect of 0.1% ofdihydrazine oxalate is very pronounced and 1s almost as great as that of1.0% lof the oxalate.

Example XI The ability of dihydrazine oxalate to rmup stocks was furtherdemonstrated by placing a raw calender-ed blank control stock and anidentical stock into which had been milled 0.1 part of dihydrazineoxalate per 100 parts of rubber between pieces of heavy duck liner,placing a kilogram weight on the top of the pile and allowing to standovernight. At the end of the test period it was noted that the stockwhich contained the dihydrazine oxalate had been liner marked or pressedto a much lesser degree than kthe blank control. The same eiects will benoted with 0.1 part of dihydrazine sulfate.

In the following examples, numbered XII to XVII, We used dihydrazinesulfate in the form of a commercial preparation containing 26.4% ofdihydrazine sulfate and '73.6% of talc which served as a carrier. Thevalues given in these examples represent the actual dihydrazine sulfatecontent employed. The amount of talc so introduced into the rubberstocks was so small as to be neg-iV 'ligible and is not reported.

l Example XII Smoked sheet natural rubber Was milled on an open rubbermill at 300 F. in the presence and absence of dihydrazine sulfate per100 The Mooney viscosities at 212 F. were measured at intervals duringthe hot milling. The data were as follows:

approximately 0.1 part of MOONEY 'vrsoosr'rrns AT 212 iin-HOT MILLED AT300 F.'

. 12 'Ihe improvement over the blank control due to the presence of thedihydrazine sulfatey is apparent and substantial. v

Example XIII This example demonstrates the use of dihydrazine sulfate inregular GR-S and in so-called col GR-S (X-478). In line with Example VIabove, the stiffening agent is more effective in the regular GR than inthe "coldV GR-S. This i-s probably due to the resistance to break-downof the latter on a hot mill. Y f

In this example the GR-S polymers were milled on the open rubber mill at250 F. for times ranging upto l5 minutes in the presence and absence ofapproximately 0.1 part of dihydrazine sulfate per y100 parts of polymer.The data were as follows: Y

MOONEY VISCOSITIES AFTER MILLING AT 250 F.

A B C D Stock Regular GR-S Cold GR-S +0.1% of +0.1% of Blank Dihvydx'a-Blank Dihydrazine zine Sulfate Sulfate Example XIV In this example thestiiening action of dihydrazine sulfate on two types of neopreneundergoing hot milling at 250 F. was measured. The data follow:

The stilfening effect of dihydrazine. sulfate uponbutadiene-acrylonitrile rubbe'ry copolymers undergoing h'ot milling at250 F. was measured. The data follows:

l MOONEY VISCOSITIES AFTER MILLING A'Iw250" F.

A B C D Stock Nitrile Rubber A Nitrile Rubber B Y (`Paracril) +0.17 of+0.17 of Blank Dihydra- Blank Dihytirazine zine H Y Sulfate W Siulfate`Milling Time, Minutes: 1

Example XVI The stiiening'action of dhydrazine sulfate in a naturalrubbcr tread, stockwith a highcarbonblack loading I. was demonstrated inthis example. Y The amount lof dihy- Stoek A B Blank 0.1% di- Controlhydrazine sulfate Milling Time, minutes:

/drazineysulfate ranged from approximately005 'to approxlmately 0.2 partper '100 parts of rubber. Ylt'will 13 be noted from the data that almostmaximum stilening eect occurred with only 0.1 part of this chemical.

The base formula was as follows:

14 is considerably stiffer than it would have been if made in the sameway but without the use of said salt, and vulcanizing the resultingmixture.

Parts 2. The method which comprises milling into an unvul- Srnoliedsheet 100,0 5 canized rubber stock which is in process and has an ob-Medium processing channel blacl; 45.0 jectionably low viscosity forsatisfactory handling in fac- Zinc oxide 5.0 tory operations, the rubberin said stock being selected Pine tar 3.5 from the group consisting ofnatural rubber, rubbery Zinc saltsof coccoanut oil fatty acids 3.5butadiene-styrene copolymers, rubbery butadiene-acry-MSICPIODelZOhaZOIF: 1K3 lo lonitrlle copolymers, and polychloroprene,dihydrazine Sulfur 3-0 oxalate in an amount containing from 0.01 to 0.1part of actual hydrazine per 100 parts of said rubber, ex- Tbl 161-0posing the mixture to a temperature ranging from room With separateportions of the above base stoei; there temperature t a 'temperaturelust belOW that et Wbeb Were intimately incorporated varying amounts ofdihyl thermal DUI'Y T0 Said rubber would OCCHI and Thereby drazinesulfate in the same way as in Example l. The Causing Sad dhYdfaZIleoxalate t0 act UPOH Sad Stock data were as follows; in vsuch a way as tolimp-art thereto al considerably in- A B o D E Above Base Stock 161.0161.0 161. 0 ll-0 161- Dihydrazine Sulfate 0. 0" 0. 1 0- 15 0- 2 MooneyViscosities of Uncured Stock 62 8O 92 94 94- 5 UNAGED PROPERTIES (P. S.I.) OF VULCANIZATES (CURED 45 AT 274 F.)

300 lVIDduluS 940 990 1, 040 1, 000 1, 100 500% Mod111us 2, 370 2, 4502, 590 2, 530 2, 730 Break 4, 150-690 4, 370-710 4, 400-700 4, 260-7004, 330-680 T-O at 350% +0. 2 -1. 6 -1. 2 -l. 0 1. 4

Example XVII The stiiening elect of approximately 0.1% (based on rubber)of dihydrazine sulfate in natural rubber footwear stocks essentially thesame as those discribed in Example X above was determined, using typicalhot air and hot air-ammonia cured stocks. The addition of this smallamount of dihydrazine `sulfate finned up thes.n stocks suiciently toeliminate most of the processing ditculties. Thus, the adverse softeningeti'ect of working high percentages of raw scrap back into new mixtures,resulting in unduly soft, calendered stocks which blister and linermark, is easily overcome.

This application is a continuation-in-part of our copending applicationSerial No. 220,539, tiled April 1l, 1951.

Having thus described our invention, what we claim and desire to protectby Letters Patent is:

l. The method which comprises milling intoan unvulcanized rubber stockwhich is in process and has an objectionably low viscosity forsatisfactory handling in factory operations, the rubber in said stockbeing selected from the group consisting of natural rubber, rubber;butadiene-styrene copolymers, rubbery butadiene-acrylonitrilecopolymers, and polychloroprene, a. salt selected from the groupconsisting of dihydrazine oxalate and dihydrazine sulfate in an amountcontaining from 0.01 to 0.1 part of actual hydrazine per 100 parts ofsaid rubber, exposing the mixture to a temperature ranging from roomtemperature to a temperature just below that at which thermal injury tosaid rubber would occur and thereby causing said salt to act upon saidstock in such a Way as to impart thereto a considerably increasedstiiness, at some point incorporating in the stock vulcanizng and otherconventional compounding ingredients, limiting mastication afterincorporation of said salt to such an extent that the stilening eect ofsaid salt is retained to a material extent and the resulting mixturecreased stiffness, at some point incorporating in the stock vulcanizingand other conventional compounding ingredients, limiting masticationafter incorporation of said dihydrazine oxalate to such an extent thatthe stifIening elect of said dihydrazine oxalate is retained to a.material extent and the resulting mixture is considerably stiler than itwould have been if made in the same Way but without the use of saiddihydrazine oxalate, and vulcanizing the resulting mixture.

3. The method which comprises milling into an unvulcanized rubber stockwhich is in process and has an objectionably low viscosity forsatisfactory handling in factory operations, the rubber in said stockbeing selected from the group consisting of natural rubber, rubberybutadiene-styrene copolymers, rubbery butadiene-acrylo4 nitrilecopolymers, and polychloroprene, dihydrazine sulfate in an amountcontaining from 0.01 to 0.1 part of actual hydrazine per parts of saidrubber, exposing the mixture to a temperature ranging from roomtemperature to a temperature just below that at which thermal injury toSaid rubber would occur and thereby causing said dihydrazine sulfate toact upon said stock in such a way as to impart thereto a considerablyincreased stiiness, at some point incorporating in the stock vulcanizingand other conventional compounding ingredients, limiting masticationafter incorporation of said dihydrazine sulfate to such an extent thatthe stiifening effect of said dihydrazine oxalate is retained to amaterial extent and the resulting mixture is considerably stiffer thanit would have been if made in the sarne way but without the use of saiddihydrazine sulfate, and vulcanizing the resulting mixture.

References Cited in the le of this patent UNITED STATES PATENTS BusseNov. 15, 1938

1. THE METHOD WHICH COMPRISES MILLING INTO AN UNVULCANIZED RUBBER STOCKWHICH IS IN PROCESS AND HAS AN OBJECTIONABLY LOW VISCOSITY FORSATISFACTORY HANDLING IN FACTORY OPERATIONS, THE RUBBER IN SAID STOCKBEING SELECTED FROM THE GROUP CONSISTING OF NATURAL RUBBER, RUBBERYBUTADIENE-STYRENE COPOLYMERS, RUBBERY BUTADIENE-ACRYLONITRILECOPOLYMERS, AND POLYCHLOROPRENE, A SALT-SELECTED FROM THE GROUPCONSISTING OF DIHYDRAZINE OXALATE AND DIHYDRAZINE SULFATE IN AN AMOUNTCONTAINING FROM 0.01 TO 0.1 PART OF ACTUAL HYDRAZINE PER 100 PARTS OFSAID RUBBER, EXPOSING THE MIXTURE TO A TEMPERATURE RANGING FROM ROOMTEMPERATURE TO A TEMPERATURE JUST BELOW THAT AT WHICH THERMAL INJURY TOSAID RUBBER WOULD OCCUR AND THEREBY CAUSING SAID SALT TO ACT UPON SAIDSTOCK IN SUCH A WAY AS TO IMPART THERETO A CONSIDERABLY INCREASEDSLIFFNESS, AT SOME POINT INCORPORATING IN THE STOCK VULCANIZING ANDOTHER CONVENTIONAL COMPOUNDING INGREDIENTS,